The plasma membrane, also known as the cell membrane, is a thin layer of lipids and proteins that surrounds and encloses the contents of a cell. It plays an important role in maintaining the integrity of the cell and regulating the movement of substances in and out of the cell.
One key aspect of the plasma membrane is its ability to allow for diffusion, a process by which molecules move from an area of higher concentration to an area of lower concentration. This is driven by Brownian motion, the random movement of molecules due to collisions with other molecules.
Osmosis is a specific type of diffusion that occurs in liquid solutions. It is the diffusion of water molecules across a selectively permeable membrane, from an area of higher water concentration to an area of lower water concentration.
The solute is the dissolved substance in the solution, and the concentration of the solute can also affect osmosis. A higher concentration of solute will result in a lower concentration of water, and vice versa. The plasma membrane is selectively permeable, meaning it can control which molecules can pass through, which allows the cell to maintain the proper balance of water and solutes inside and outside the cell.